NASA's Mars Curiosity rover is preparing to drill into the Martian surface for the first time.

The venture marks the rover's most significant engineering test since its descent onto the red planet five months ago.

Scientists pinpointed the first rock the rover's drill piece will pierce in a region known as Yellowknife Bay, which was once saturated with water.

"Drilling into a rock to collect a sample will be this mission's most challenging activity since the landing," said project manager Richard Cook, from NASA's Jet Propulsion Laboratory in Pasadena, California.

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"It has never been done on Mars," he said.

One of the rover's tasks during its two-year mission is to determine whether Mars is, or ever was, habitable. Studying the planet's geology provides scientists with important clues.

Curiosity is currently exploring a region surrounding the target rock, and if the structure meets the engineers requirements, the NASA team hope to use the drill in the next two weeks.

The rock, named after the former Mars Science Laboratory deputy project manager John Klein, who died in 2011, was selected because it had a different type of wet environment than the streambed where the rover landed.

Curiosity's cameras have found some unexpected features in the area's rock formations, including veins, cross-bedded layering, and pebbles embedded in sandstone.

The Mars Science Laboratory's project scientist John Grotzinger said the veins suggested water had percolated through the rocks, leaving behind minerals, likely calcium sulfate.

"This is the first time in this mission that we've seen not just an aqueous environment but one that has precipitated minerals," said Professor Grotzinger from the California Institute of Technology.

The team are hoping the drill, which can burrow to a depth of five centimetres, will sample material from the veins and surrounding rocks.

"[That will] give us an appraisal of the habitability of this environment," he said.

The rover's Mars Hand Lens Imager (MAHLI) has also examined nearby sedimentary rocks, which form when material is deposited by water, of varying shapes and sizes.

Some rocks had grains the size of peppercorns; while others had grains the size of powdered sugar.

"All of these are sedimentary rocks, telling us Mars had environments actively depositing material here," said the MAHLI deputy principal investigator Aileen Yingst, from the Planetary Science Institute in Tucson, Arizona.

"The different grain sizes tell us about different transport conditions."

Curiosity's findings will serve as a foundation for the agency's plans to send humans to Mars in the mid-2030s.